Originally built to prevent saltwater moving upstream, it now keeps the river level through Geelong and is an important crossing point.
 
Construction on the weir started in late 1838 under Captain Foster Fyans and was completed by May 1840. Built by convicts, the weir failed in flood in 1844, not being fully rebuilt until 1849. Little changed to the breakwater until it was rebuilt by the Country Roads Board for modern traffic in the mid 1960's.